/Engine/Source/Developer/TargetPlatform/Public/Interfaces/ITargetPlatformManagerModule.h
A callback that holders of ITargetPlatform* must subscribe to to be notified of when the ITargetPlatform* has been invalidated and should be requeried from e.g. FindTargetPlatform
[FOnTargetPlatformsInvalidated](API\Developer\TargetPlatform\Interfaces\FOnTargetPlatformsInvalidated) & GetOnTargetPlatformsInvalidatedDelegate()